Delft University of Technology
Self-organizing avulsions in an endorheic dryland river system
Donselaar, Rick; Cuevas Gozalo, M.C.; van Toorenenburg, K.A.; Wallinga, J.
Publication date 2018
Document Version
Accepted author manuscript
Citation (APA)
Donselaar, M. E., Cuevas Gozalo, M. C., van Toorenenburg, K. A., & Wallinga, J. (2018). Self-organizing avulsions in an endorheic dryland river system. Abstract from 20th International Sedimentological Congress 2018, Québec, Canada.
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ISC2018, Québec City
SELF-ORGANIZING AVULSIONS IN AN ENDORHEIC DRYLAND
RIVER SYSTEM
M.E. Donselaar1,2,*, M.C. Cuevas Gozalo3, K.A. van Toorenenburg1, J. Wallinga4
1Department of Geoscience and Engineering, Delft University of Technology, Stevinweg 1, 2628 CN Delft, The
Netherlands
2KU Leuven, Department of Earth and Environmental Sciences, B-3001 Leuven-Heverlee, Belgium 3Brill, Plantijnstraat 2, 2321 JC Leiden, The Netherlands
4Netherlands Centre for Luminescence dating & Soil Geography and Landscape group, Wageningen University, PO
Box 47, 6700 AA Wageningen, The Netherlands *e-mail: m.e.donselaar@tudelft.nl
Absolute age dating with Optically Stimulated Luminescence (OSL) measurements, in combination with Google Earth Pro imagery and differential GPS (dGPS) measurements was employed to unravel the processes and timing of river avulsions and the resultant sedimentary architecture of a network of Holocene Río Colorado (Altiplano Basin, Bolivia) channel belts. A radial pattern of channel belts originated from compensational stacking of interconnected alluvial ridges. Channel-belt switching occurred by avulsions with frequencies ranging from 160 yr to 1130 yr. Rivers started with a low-sinuous (SI 1.29 to 1.64) single-channel trajectory bordered by small point bars. Over time, the rivers evolved to high-sinuous (SI 1.80 to 2.29) streams with wide point bars with a large surface area. The average lateral point-bar accretion rate is 0.5 my-1.
The alluvial ridges formed by river sediment accumulation through aggradation and lateral accretion of sand in point bars, channel-floors, and levees, and by lateral amalgamation and stacking of crevasse splays. The width of the individual ridges in the study area is approximately 1.5 km. Confined inter-channel areas received crevasse splay sediment from both sides of successive channel-belt positions, and the overlapping crevasse-splay sand resulted in a higher inter-ridge elevation as compared to the unconfined side where the alluvial ridge bordered the open floodplain. Alluvial-ridge aggradation resulted in decrease of the along-river gradient and increase of cross-floodplain gradient, to the point where the channel-floor elevation became higher than the surrounding floodplain surface, whereupon avulsion occurred, and the process of alluvial-ridge growth started anew. Successive channel belts avoided the positive morphology of earlier-deposited alluvial ridges and thus formed a self-organizing, laterally-connected alluvial-ridge network over an area of 500 km2.
Acknowledgements
Financial support for the research from Wintershall Noordzee B.V., Energie Beheer Nederland (EBN) and ENGIE E&P Nederland B.V. is gratefully acknowledged. Alice Versendaal of the Netherlands Centre for Luminescence dating (NCL) at Wageningen University is thanked for the OSL measurements and analyses. The Netherlands Organization for Scientific Research (NWO-ALW) supplied the investment grant (#834.03.003) for the OSL laboratory.
